Endothelial cell growth inhibitor (EGI) is a protein produced by capillary endothelial cells which inhibits their growth in an autocrine fashion. EGI will be purified from growth medium conditioned by endothelial cells and used in in vitro and in vivo model systems to test whether this protein can be used to inhibit the formation of new capillaries. This is the first step towards developing a therapy that will be used in the treatment of solid tumors, various retinopathies, psoriasis, arterial occlusive disease and in birth control, all of which either involve neovascularization or growth of endothelial cells themselves.